During the Georgian era (from 1714 to 1830), new districts like Mayfair formed, and new bridges over the Thames encouraged development in South London.

The city continued to rise to the global empire that it is today.

Mexico City, originally named Tenochtitlán, was founded under the Aztec Empire in 1325.

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Spanish explorer Hernán Cortés landed there in 1519, and conquered it soon after. Tenochtitlán was renamed "Mexico" in the 15th century, because the Spanish found it easier to pronounce.

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Mexico City instituted a grid system (which is how many colonial Spanish cities were set up) starting in the 16th century, with the Zócalo as the main square.

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In the late 19th century, the city started developing a modern infrastructure, including roads, schools, and public transport — though many of these resources were concentrated in wealthy areas.

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Mexico City grew upwards in the 1950s with the construction of the Torre Latinoamericana — the city's first skyscraper.

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Today, Mexico City is a vibrant home to over 8.9 million people.

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Moscow was founded in the 12th century. By the 17th century, the Tsars (aka Slavic monarchs including Ivan IV and the Romanovs) were in charge.

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The city grew around the Moskva river.

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Street vendors set up around the Kremlin.

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The world-famous St. Basil's Cathedral was completed in 1561, and it continues to wow visitors with its historic charm...

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... while Moscow gets more cutting-edge every year.

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The region near today's Johannesburg was originally inhabited by the San people, an indigenous group of hunter-gatherers, roughly 20,000 years ago. In the 13th century, Bantu-speaking people moved to the area, formed small villages, farmed, and mined for iron.

A gold basin, called Witwatersrand, was discovered in 1884, which attracted many Europeans to the area. Today, the basin holds the world's largest known gold reserves and has produced over 1.5 billion ounces of the precious metal.

A 1902 map of Witwatersrand in Johannesburg.The National Library of France

Around this time, the city was named Johannesburg — though historians don't know exactly why. The city's earliest records, which may have offered information about its etymology, is lost.